The present invention relates to universal switching power supplies, and more specifically to intrinsically safe universal switching power supplies. Intrinsically safe power supplies are particularly useful in petroleum and chemical industries.
Switching power supplies are commonly used throughout the world in computers and many other apparatus. They are used because, for the same output power, they are much smaller and lighter. Switching power supplies also provide a good regulation of the outputs over a wide range of input voltages. Isolated 90 to 250 Vac switching power supplies are quite common in the art. Isolated DC to DC switching power supplies with an input voltage range of 9 to 35 V are also quite common in the art.
Around the world, there are many voltage standards employed for powering electrical equipment. For instance, there are 9 Vac/Vdc, 12 Vac/Vdc, 24 Vac/Vdc, 48 Vdc/Vac, 90-250 Vac and some 129 Vdc standards. In addition, there are probably many other very special cases used around the world. There remains a need for a universal power supply that handles 9-250 Vac and Vdc.
In some chemical and petroleum industries, there is a need for a very high level of safety to make sure that the output is well isolated and won""t create any risk of flame, explosion or shock hazard. Power supplies of this type are commonly referred to as intrinsically safe (I.S.) power supplies. In fact, most of the time, only one of the power supply outputs is considered I.S.
To build an I.S. transformer, the transformer must have a large spacing with redundant protections to allow two faults anytime and anywhere in the power supply electronic circuit. With a normal frequency transformer, the required spacing is achieved by using separate bobbins on the same core. But when building a switching power supply, a high switching frequency must be used. This also means a much smaller inductance on each winding. To achieve a small inductance, the entire transformer is forced to be much smaller, and thus such a large spacing is almost impossible even with separate bobbins.
Accordingly, there also remains a need for an intrinsically safe universal switching power supply.
The present invention provides an intrinsically safe switching power supply able to cover 9-250 Vac, 40-70 Hz and 9-250 Vdc on the same power cord. The power supply provides outputs of xe2x88x9212V, +5V, +12V, +24V all referred to the earth ground. These voltages are available for digital and analog circuit purposes. The power supply may also generate an isolated 5V output for RS-485 communication applications. The xe2x88x9212V and +12V outputs include an intrinsically safe isolation for an I.S. milliamp output circuit. All the rails are isolated from the input voltage.
To obtain an isolated output while meeting the spacing/layout requirements according to CENELEC standards (EN 50020) and to comply with the international safety standard (IEC 1010-1) to get CSA and FM approvals, according to another aspect the switching power supply according to the present invention includes a transformer with a multi-layer PCB. Utilizing a multi-layer PCB, the spacing requirements are obtained by laying out windings for the transformer within the PCB board/layers. The core for the transformer may comprise a standard planar core.
According to another aspect of the invention, a very wide range of voltages is obtained by including circuitry to produce very narrow pulses to control a MOSFET that switches the transformer.
The power supply according to the present invention comprises one or more of the following features:
(1) an alternating and direct current capability (ac/dc).
(2) an input voltage range which is controlled by the electronics for the full ac/dc range and is transparent to the user, i.e. without the need for a manual voltage range selecting switch.
(3) a maximum input voltage and a minimum input voltage ratio having a factor equal or greater than 7.3.
(4) a fly-back (step-up) topology.
(5) a duty cycle controller capable of providing 10 ns to 7 us pulse outputs.
(6) circuitry for creating the equivalent of a very low impedance MOSFET transistor at low voltage and a quick low stray capacitance MOSFET transistor at high voltage.
(7) at least one intrinsically safe voltage output comprising a PCB transformer and a planar core.
In a first aspect, the present invention provides a switching power supply for generating one or more voltage outputs, and one of the voltage outputs comprising an intrinsically safe voltage output, said switching power supply comprising: (a) an input stage having an input for receiving a supply voltage and a circuit for converting said voltage to a DC level; (b) a first stage coupled to said input stage for receiving said DC level and said first stage having a circuit for generating an output voltage from said DC level; (c) a second stage coupled to said first stage and having a circuit for receiving said output voltage produced by said first stage and including circuitry for generating one or more voltage outputs and an intrinsically safe voltage output; (d) a planar core transformer for isolating said second stage from said first stage; (e) said first stage including primary windings electromagnetically coupled to said planar core transformer, and said primary windings comprising a plurality of conductive tracks formed on a layer of a multi-layer circuit board; (f) said second stage including secondary windings electromagnetically coupled to said planar core transformer, and said secondary windings comprising a plurality of conductive tracks formed on another layer of said multi-layer circuit board, and said secondary windings including windings formed as a plurality of conductive tracks for generating said intrinsically safe voltage output, and said other layer being isolated from said layer carrying said conductive tracks for said primary windings.
In a second aspect, the present invention provides an intrinsically safe switching power supply for generating one or more voltage outputs, said switching power supply comprising: (a) a circuit board having a plurality of layers, and including an opening for receiving a transformer; (b) a first stage having an input for receiving a supply voltage and including a converter circuit for converting said supply voltage to a DC level and having circuitry for producing an output voltage from said DC level, and said first stage including primary windings, said primary windings being formed as conductive tracking on one layer of said circuit board; (c) a second stage coupled to said first stage through said transformer and said second stage including secondary windings for coupling said output voltage produced by said first stage through said transformer, said second stage including circuitry for generating one or more voltage outputs, and said secondary windings being formed as conductive tracking on another layer of said circuit board, and said circuit board including an output layer for said voltage outputs; (d) said second stage including a sub-stage for generating an intrinsically safe voltage output, and said sub-stage comprising a plurality of separate secondary windings for coupling said output voltage produced by said first stage and circuitry for generating said intrinsically safe voltage output, and said separate secondary windings comprising conductive-tracking formed on another layer of said circuit board, and said layer carrying the conductive tracking for said intrinsically safe voltage output being isolated from said other layers in said circuit board.
In another aspect, the present invention provides a switching power supply for generating one or more voltage outputs, said switching power supply comprising: (a) an input stage having an input for receiving a supply voltage and a circuit for converting said voltage to a DC level; (b) a first stage coupled to said input stage for receiving said DC level and said first stage having a circuit for generating an output voltage from said DC level; (c) a second stage coupled to said first stage and having a circuit for receiving said output voltage produced by said first stage and including circuitry for generating one or more voltage outputs and an intrinsically safe voltage output; (d) a planar core transformer for isolating said second stage from said first stage; (e) said first stage including primary windings electromagnetically coupled to said planar core transformer, and said primary windings comprising a plurality of conductive tracks formed on a layer of a multi-layer circuit board; (f) said second stage including secondary windings electromagnetically coupled to said planar core transformer, and said secondary windings comprising a plurality of conductive tracks formed on another layer of said multi-layer circuit board, and said other layer being isolated from said layer carrying said conductive tracks for said primary windings; (g) said circuit for generating an output voltage in said first stage including a switching device and a controller coupled to said switching device, said switching device being coupled to said primary windings, and said switching device switching a current through said primary windings under the control of said controller.
In a yet another aspect, the present invention provides a switching power supply for generating one or more voltage outputs, and one of the voltage outputs comprising an: intrinsically safe voltage output, said switching power supply comprising: (a) an input stage having an input stage for receiving a supply voltage and a circuit for converting said supply voltage a DC level input; (b) a first stage coupled to said input stage for receiving said DC level and said first stage having first stage circuit for producing an output voltage from said DC level; (c) a second stage coupled to said first stage and having a circuit for receiving said output voltage produced by said first stage and including a circuit for generating one or more voltage outputs and an intrinsically safe voltage output; (d) a planar core transformer for isolating said second stage from said first stage; (e) said first stage including primary windings electromagnetically coupled to said planar core transformer, and said primary windings comprising a plurality of conductive tracks formed on one layer in a multi-layer circuit board; (f) said second stage including secondary windings electromagnetically coupled to said planar core transformer, and said secondary windings comprising a plurality of conductive tracks formed on one or more layers in the multi-layer circuit board; (g) a start-up stage coupled to said first stage and said input stage, said start-up stage including means for starting said power supply during a low period.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.